Final answer:
ADP is central to oxidative phosphorylation, serving both as a substrate for ATP synthesis via ATP synthase and as a regulator for the rate of electron transport based on cellular ATP demand.
Step-by-step explanation:
Adenosine diphosphate (ADP) plays a critical role in the process of oxidative phosphorylation, which is the primary method for producing adenosine triphosphate (ATP) during cellular respiration. When glucose is catabolized, most of the ATP is generated through chemiosmosis that occurs within the mitochondria in eukaryotic cells and the plasma membrane of prokaryotic cells. Energy from the electron transport chain is used to phosphorylate ADP to ATP, with oxygen being necessary for this process. ADP acts as a substrate for ATP synthase, which adds a phosphate group to ADP to form ATP. The concentration of ADP in the cell serves as a regulator for the electron transport chain; higher levels of ADP indicate greater ATP consumption and trigger the chain to speed up.
The rate of oxidative phosphorylation is affected by levels of ADP and ATP - a build-up of ADP due to increased ATP consumption signals the cell to activate the electron transport chain to produce more ATP. Conversely, when energy demand is low, and ATP builds up, the electron transport chain is slowed down. This feedback mechanism ensures that the supply of ATP matches the energy demands of the cell.
Additionally, ADP and AMP can act as positive allosteric modulators for various enzymes involved in energy-yielding reactions, further illustrating the essential role that ADP plays in cellular metabolism.